The update will show up for all users with all versions of the .NET framework, so if you're on a desktop system that doesn't do web serving it's not a really high priority to apply the update. In fact, one could argue that it doesn't really matter for desktops, unless they are running development IIS web servers and those servers are available to untrusted users.

For servers it's a clearly important update, but not of the "drop everything and apply this now" type. You should test it. And if you don't do .NET applications on the server you shouldn't need it (but then you shouldn't need the .NET Framework either).

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